The present invention relates in general to data transfer in a telecommunications network and more particularly to a method and apparatus for passing control information in a bidirectional line switched ring configuration.
In conventional telecommunications networks, service providers have deployed Bidirectional Line Switched Rings (BLSR) to provide a network restoration capability. In a BLSR configuration, a node couples to other nodes in the system by a working communication link and a protection communication link set up in a dual ring topology. Traffic and other information travels around the working communication link and is extracted by a node in response to the node being the desired destination. The protection communication link provides another path to transfer the traffic and other information in the event of a failure in the working communication link between any node in the system. The BLSR configuration provides network survivability for single link failures and allows the network to function in a segmented mode when entire nodes have failed.
One feature that digital cross connect systems bring to the BLSR configuration is that they can act as nodes on the BLSR for passing traffic between east and west ring port interfaces as well as providing the restoration switching function. By means of their cross connect matrices, the digital cross connect systems may provide protection channel access during normal ring operation and ring interconnections.
In order for a BLSR to properly function and monitor the status of all its nodes, two bytes of information, designated K1 and K2, must pass through the protection communication link. By its nature, a digital cross connect system at a node allows east and west ring port interfaces to be connected by its cross connect matrix.
However, in the event that protection channel access is desired at a node, there is no dedicated connectivity through the cross connect matrix between the east and west ring port interfaces to pass the K1/K2 bytes, especially if 100% of the working traffic is dropped at the node. Therefore, it is desirable to be able to pass the K1/K2 and through a node while still providing protection channel access at the node.
From the foregoing, it may be appreciated by those skilled in the art that a need has arisen for a technique to pass control information in a bidirectional line switched ring configuration while still providing total protection channel access. In accordance with the present invention, a method and apparatus for passing control information in a bidirectional line switched ring configuration are provided which substantially eliminate or reduce disadvantages and problems associated with conventional bidirectional line switched ring topologies.
According to an embodiment of the present invention, there is provided a cross connect system in a telecommunications network that includes a first ring port interface operable to receive and provide traffic information from and to a working communication link and control information from and to a protection communication link of a fiber optic ring. The control information is associated with the traffic information. A first add/drop unit receives traffic information carried on the working communication link from the first ring port interface and destined for the cross connect system. A first protection channel access unit receives control information from and provides control information to the protection communication link through the first ring port interface. A second ring port interface receives and provides traffic information from and to a working communication link and control information from and to a protection communication link of a fiber optic ring. A cross connect matrix passes traffic information and control information between the first add/drop unit and the first ring port interface, between the first protection channel access unit and the first ring port interface, and between the first ring port interface and the second ring port interface. The cross connect matrix provides a dedicated communication path for the control information to pass from the first ring port interface to the second ring port interface.
The present invention provides various technical advantages over conventional bidirectional line switched ring topologies. For example, one technical advantage is to provide a capability to pass control signals when a node has a protection channel access capability. Another technical advantage is to provide an efficient and inexpensive fixed connection for the protection channel through a cross connect matrix. Yet another technical advantage is to avoid creating and deleting connections based on ring activity. Other technical advantages may be readily apparent to those skilled in the art from the following figures, description, and claims.